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Aloe reitzii var. reitzii is a summer-flowering (February–March) succulent, endemic to a restricted range within the heavily transformed grasslands of eastern South Africa. Floral structure and nectar properties suggest bird-pollination. This study investigated the temporal visitation events of birds to this aloe. Extensive camera observations during the 2017 flowering season (23 days) identified both specialist and generalist nectarivorous birds (n = four and five species respectively) as regular diurnal aloe visitors. Malachite Sunbirds (Nectarinia famosa) accounted for 49% of all visits, while Cape Weavers (Ploceus capensis) made up 41% of all visits; these species co-dominate visitation of the specialist and generalist avian feeding guilds respectively. In addition, visitation by each guild was separated temporally to some extent, with generalists mostly visiting early in the day, while specialists dominate afternoon visitation. Nectar volume (overall unbagged mean = 48.67 ± 4.70 µL) and concentration (overall unbagged mean = 10.68 ± 0.21% w/w) remains consistent throughout the day, and are within generalist nectar-feeding bird preferences, which may explain the abundance of Cape Weavers, despite floral morphological traits matching those of specialist nectar feeders. While many summer-flowering aloes are primarily insect- or sunbird-pollinated, Cape Weavers may be supplementing their diets with A. reitzii var. reitzii nectar, and potentially playing a crucial role in pollination.

Parthenium hysterophorus L. (Asteraceae) is a noxious, annual invasive herb prevalent in more than 50 countries worldwide. In South Africa, the weed is a highly damaging invasive species, particularly in savanna regions, threatening food security, native biodiversity, livelihoods and human health. Given the multitude of threats posed by P. hysterophorus, this study aimed to determine the influence of the invasion of P. hysterophorus and its associated seedbank dynamics at a small spatial scale. To assess this, two neighbouring savanna reserves, with differing stocking densities (i.e. over- and understocked), were selected and assessed seasonally over a four-year period. Overstocking exacerbated the invasion of P. hysterophorus, with greater densities, larger plants and increased seed production, at a plot level. This enhanced invasion was also reflected in changes to the site's above-ground plant community, with significantly lower species richness, evenness, and diversity. Parthenium hysterophorus comprised more than 80% of the overstocked reserve's seedbank, and was responsible for continued declines in the richness, evenness and diversity of species below-ground. Whereas P. hysterophorus at the understocked reserve, occupied a smaller proportion of the seedbank (∼70%), with richness, evenness and diversity all showing signs of recovery over the four-year period. Overall, this research highlighted the impacts of P. hysterophorus in South Africa, as well as the potential role grazing management has in limiting or facilitating P. hysterophorus invasions and their impacts within savannas.

Floral nectar is an important attractant and reward for visitors, and is often produced in synchrony with peak activity of pollinators. Aloe peglerae flowers in winter, and previous studies have shown that it is pollinated primarily by diurnal generalist birds, with small mammals making additional contributions to pollination at night. Nectar produced during the day is the main attractant and reward for birds, but the nectar rewards available to small mammals are unknown. This paper investigates nectar availability in Aloe peglerae, because small mammals may be feeding on remaining, or freshly produced, nectar at night. Nectar availability over a 24-hour period was measured in screened and unscreened plants (n = ten plants per treatment), and the associated partitioning of visits by diurnal birds and nocturnal small mammals assessed. Nectar is constantly available over 24-hours, but in different quantities. Nectar volume of screened (nectar availability) and unscreened (standing crop) plants, is significantly higher early in the morning after sunrise, compared with all other sampling periods during the 24-hour period. Nectar concentration did not vary over 24-hours, averaging 11.5 ± 0.4% w/w (unscreened) across the entire 24-hour period. Peaks in visits by different guilds occurred at periods (i.e. diurnal birds and nocturnal small mammals) when nectar availability was high. Aloe peglerae has higher daytime nectar production, when its primary pollinators are most active, but the continual, albeit reduced, nectar availability at night attracts small mammals. Mobile diurnal birds, and less-mobile nocturnal small mammals, both rely on this nectar resource during dry and cold South African winters and, in turn, are important pollinators for this Critically Endangered Aloe species. Keywords: Aloe peglerae, bird pollination, nectar availability, small mammal pollination, temporal partitioning

Communal livestock grazing is expected to impact botanical composition and plant diversity of Drakensberg montane grasslands. Accordingly, a grazing gradient extending outward from kraals, and fence-line contrasts between communal rangeland and protected areas (Golden Gate Highlands National Park and Royal Natal National Park), were studied in the QwaQwa region of South Africa. Presence of a grazing gradient was confirmed by a decrease in the amount of cattle dung with increasing distance from kraals that was independent of altitude, solar radiation, slope, or soil physico-chemical properties. Canonical correspondence analysis confirmed thatgrazing intensity had a significant influence on botanical composition although most compositional variation was unexplained. Higher grazing intensities tended to negatively affect plant species richness and diversity, and the cover of perennial graminoids, but benefitted the abundance of dwarf shrubs and alien invasive species. Similar effects were apparent across each of the fence line contrasts. Despite a long history of livestock grazing, communal rangeland supported >320 indigenous species, illustrating some contribution to biodiversity conservation, but being compromised near kraals. An improved approach for study of the impacts of livestock grazing on plant diversity is suggested that would overcome the difficulties of assessing rare and threatened species using acommunity approach. Keywords: communal rangelands, fence line contrast, functional types, grazing gradients

Rural households have established various informal strategies to cope with unanticipated shocks. These existing coping strategies are receiving renewed interest, particularly in the context of climate change and in terms of the role they do, and can play, in enhancing households' adaptive capacity. An improved understanding of these strategies, and the factors that influence their application, may support the design of locally relevant adaptation strategies. We explored the nature and prevalence of unanticipated shocks, including natural hazards, experienced by households in two villages in Venda, South Africa, with the villages selected, in part, because of notable differences in precipitation. We considered the influence of shock type, and household- and location-specific characteristics, on the use of various household-level coping strategies. We report on semi-structured interviews, administered to 170 randomly selected households, and a participatory rural appraisal. Almost 90% of households reported the experience of at least one unanticipated shock over a prescribed 5-year period, with natural hazards reported by 42%. The type of shock experienced and various household-level characteristics, such as households' access to human and financial capital, influences households' coping response. Households' access to natural and social capital allowed for the protection of ex-ante coping options. Overall, our findings indicate that when possible, households actively manage their coping strategy portfolio, both in response to the shock experienced and in anticipation of future shocks. Generally, households' informal, ex-post coping options appear to be insufficiently robust for the covariate nature of natural hazards, suggesting the need for interventions that support households’ existing coping portfolio.

Competition and facilitation vary inversely along environmental stress gradients. Here we ask how environmental stress along a slope gradient influences plant-plant interaction in a semi-arid savanna. We attempted to link spatial patterns and ecological interactions, so we analysed the spatial distribution of three Vachellia (Acacia) tree species and assessed the consequences of their interaction on plant structural variables (height, basal area, biomass and canopy cover) at Matopos Research Station, Zimbabwe. Spatial patterns among and between the tree species were assessed using both univariate and bivariate analysis. To understand the extent of tree species isolation, we applied the species mingling index. Canopy cover varied significantly between species at both ends of the stress gradient, while basal area did not differ among the three species at any slope position. The woodland showed differential recruitment levels for the three species across the catena, which may indicate future changes in composition. The mingling index showed that there was species isolation in the bottom and middle catena. Pair-wise interactions of plants reflected two common spatial patterns, clustering, interpreted as suggesting facilitation, and random, interpreted as neutral. In some cases these patterns changed with spatial scale, indicating that the stress gradient hypothesis (SGH) may be influenced by the spatial scale at which species are interacting. Our univariate analyses corroborate the evidence that plants in semi-arid environments have a clustered distribution and that catenas can produce differential recruitment levels of the different species.

Annual growth rings are absent in many long-lived grassland geoxyles. Thus, estimates of age for individuals are largely based on non-benchmarked assessments by experienced botanists. We wished to obtain a more precise estimate of age from the xylopodia of four geoxylic taxa (i.e. Berkheya insignis, Callilepis laureola, Protea simplex and Tephrosia kraussiana) growing in a Pondoland grassland, using both the gas proportional counting and Accelerated Mass Spectroscopy radiocarbon dating techniques. Plants sampled in 2008 fell within modern concentrations of carbon 14; therefore, radiocarbon dating generally yielded two ages for each plant, an older age (range: 45–51 years, mean=49, CV=3.6%) corresponding with the nuclear testing period, and a younger age (range: 10–29 years, mean=18, CV=35%), corresponding to the period after the Partial Nuclear Test Ban Treaty. Hence the older ages are much less variable than the younger ages. All plants had the older age estimate, and all but two had the younger age estimate. In addition, two plants each, had two similar older age estimates. P. simplex plants were 16, 24, 27 and 29, or 45, 46–49, 47 and 49 years, T. kraussiana 13, 15 and 16, or 50 and two of 51 years, C. laureola 12, 15 and 21, or 49–50 and two of 50 years and B. insignis were 10, or 49, 50 and 51 years old. Growth rings were not visible with the naked eye. However, using stereomicroscopy, ring-like patterns were visible to some extent at 7X magnification for B. insignis, P. simplex and T. kraussiana, but not C. laureola. Counts of these structures were much lower than the younger 14C dates, and hence are unlikely to be annual rings. Despite the ambiguity of multiple ages, these estimates are a useful starting point or benchmark for future empirical investigations of age for forbs with no clear annual rings. Most studies have used radiocarbon dating to estimate the age of woody tree stem tissue, whereas this study is one of few to measure the age of below-ground modern tissues of South African forbs. Suggestions for further refinement during collection and processing of geophytic sample material are made based on lessons learned from this investigation.

This is the first study documenting the distribution and population biology of the Endangered Aloe lettyae, an endemic to the highly threatened Woodbush Granite Grassland (WGG) in Limpopo Province, South Africa. We documented 19 A. lettyae populations and calculated the total area of occupied habitat at 17.5 ha within its extent of occurrence of 123 km2. Most populations were clustered on the south western side of the WGG, with all known localities less than 40 km apart in this severely fragmented vegetation type. Population size varied from 10 to 6547 plants, with ∼10,800 individuals estimated in total. Plant size and life history stage demographics were determined in seven of the 19 currently known A. lettyae populations, including two large populations, as well as a high- and a low-lying population, and constituted a representative sample of the entire geographical range of the species. For plant size, four metrics (number of leaves, number of leaf layers, height and diameter of the leaf rosette) were recorded for each sampled A. lettyae plant, and the presence of an inflorescence indicated its reproductive status. By means of the classification tree technique CHAID (Chi-square Automatic Interaction Detection), we determined that of the four plant size metrics, the ‘number of leaves’ predicts A. lettyae’s life history stages and fecundity most accurately, and revealed significant differences in the life history stage structure of the seven surveyed populations. Five populations occurring in relatively undisturbed WGG fragments, including the two large populations, comprised high proportions of adult individuals (77–89%), while only few A. lettyae juveniles were found (3–14%). By contrast, the relatively high percentage of juveniles (25–58%) and low percentage of adults (32–63%) observed in two small populations found in a degraded WGG fragment and in non-natural habitat respectively, appeared atypical. The percentage of subadults varied little across the surveyed populations (8–13%). In slow-growing, long-lived species such as A. lettyae, the dominance of adult individuals with a high probability of survival may be considered as indicative of stable populations. This study provides baseline A. lettyae population data for long-term demographic monitoring which will aid management and conservation of the range restricted, Endangered A. lettyae.

There is evident variation in body size amongst Anthonomus santacruzi Hustache, 1924, weevils. The aims of this study were to assess if the variation in body size in A. santacruzi weevils is a result of sexual dimorphism and what features can be used to distinguish males from females. The weevils were collected from field sites in Mpumalanga, South Africa, where they were introduced as biocontrol agents of Solanum mauritianum Scopoli. Body structures and the presence/absence of the tergal notch was examined under an optical stereomicroscope and SEM to assess differences between sexes. The morphometric analysis of the body structures included rostrum length (base–apex and antennal insertion–apex), elytral length and width, pronotum length and width, first tarsus length, first tibia length, funiculus length and total body length. Rostrum length, elytra length and width and total body length were significantly larger in females than in males. A tergal notch in the 8th abdominal tergite was present in males and absent in females. The body structure; of rostrum length, elytra length and width and total body length overlapped between sexes in some specimens. The abdominal tergal notch was found to be the most useful body structure to distinguish males from females in A. santacruzi.

African termites are classified into five distinct families, Termitidae, Rhinotermitidae, Hodotermitidae, Termopsidae and Kalotermitidae. Termites are undoubtedly one of the key ecosystem engineers...

Background The noxious annual herb, Parthenium hysterophorus L. (Asteraceae), is an invasive weed of global significance, threatening food security, biodiversity and human health. In South Africa, chemical control is frequently used to manage P. hysterophorus, however, concern surrounds increasing atmospheric CO2 levels, which may reduce the efficacy of glyphosate against the weed. Therefore, this study aimed to determine the susceptibility of P. hysterophorus to glyphosate (1L/ha: recommended) after being grown for five generations in Convirons under ambient (400 ppm) and elevated (600 and 800 ppm) CO2 . Results Glyphosate efficacy decreased with increasing CO2 , with mortalities of 100, 83 and 75% recorded at 400, 600 and 800 ppm, respectively. Parthenium hysterophorus experienced enhanced growth and reproduction under elevated CO2, however, glyphosate application was highly damaging, reducing the growth and flowering of plants across all CO2 treatments. Physiologically, glyphosate-treated plants, in all CO2 treatments, suffered severe declines of >90% in chlorophyll content, maximum quantum efficiency (F v /Fm ), photon absorption (ABS/RC), electron transport (ET 0 /RC) and performance index (PI ABS ), albeit at slower rates for plants grown under elevated CO2 . Low levels of recovery from glyphosate were documented only for plants grown under elevated CO2 and was attributed to their increased biomass. Conclusion These results suggest that increasing CO2 levels may hinder chemical control efforts used against P. hysterophorus in the future, advocating for further investigation using multigenerational CO2 studies and the maintenance of effective spraying programs at present. © 2020 Society of Chemical Industry.

Lantana camara L. (Verbenaceae) is a weed of significant concern in many tropical and subtropical countries. This work aimed to quantify the combined impact of the established suite of lantana biocontrol agents on plant growth under field conditions in an inland area with a continental climate in South Africa. An insecticidal exclusion method was employed to compare plant growth parameters and agent damage between exclusion plants and biocontrol plants. Despite failing to maintain exclusion plants completely biocontrol agent-free, leaf damage was 44% greater, and side-stem production 16% less, in biocontrol compared to exclusion plants. There was a positive relationship between leaf damage and reduction in side-stem production over the study period. Overall, insecticidal exclusion, though only partially effective, showed that the established suite of lantana biocontrol agents is having a measurable growth-inhibitory impact on the target weed.

Two biocontrol agents, a leaf-spot pathogen, Passalora ageratinae, and a stem gall fly, Procecidochares utilis, have been released against Crofton weed, Ageratina adenophora (syn. Eupatorium adenophorum) (Asteraceae), in South Africa. This work reports the first post-release evaluation of the effect of both agents acting together in the field. A greenhouse trial using both agents had predicted an additive (beneficial) interaction between the agents. This study investigated if the additive interaction was present in the field. Four month old stems were exposed to one of the following three treatments (n = 20 plants per treatment): pathogen-only, pathogen plus single fly-galled, and pathogen plus double fly-galled, for 11 months. The interaction between the agents was equivalent to both agents acting independently (i.e. there was no additive effect on the weed’s growth). The greenhouse trails were therefore not predictive of field conditions.

This laboratory-based study sought to determine the efficacy of using carbofuran in an exclusion experiment aimed at assessing the impacts of biocontrol agents on Lantana camara L. (sensu l...

Background and AimsFine-scale spatial patterns of the seedlings of co-occurring species reveal the relative success of reproduction and dispersal and may help interpret coexistence patterns of adult plants. To understand whether postfire community dynamics are controlled by mathematical, biological or environmental factors, we documented seedling–adult (putative parent) distances for a range of co-occurring species. We hypothesized that nearest-seedling-to-adult distances should be a function of the distance between the closest conspecific seedlings, closest inter-adult distances and seedling-to-parent ratios, and also that these should scale up in a consistent way from all individuals, to within and between species and finally between functional types (FTs).MethodsWe assessed seedling–adult, seedling–seedling and adult–adult distances for 19 co-occurring shrub species 10 months after fire in a species-rich shrubland in south-western Australia. Species were categorized into 2 × 2 FTs: those that are killed by fire [non-(re)sprouters] vs. those that survive (resprouters) in nine taxonomically matched pairs, and those that disperse their seeds prefire (geosporous) vs. those that disperse their seeds postfire (serotinous).Key ResultsFor the total data set and means for all species, seedling–adult distance was essentially a mathematical phenomenon, and correlated positively with seedling–seedling distance and adult–adult distance, and inversely with seedlings per adult. Among the four FTs, seedling–adult distance was shortest for geosporous non-sprouters and widest for serotinous resprouters. Why adults that produce few seedlings (resprouters) should be further away from them defies a simple mathematical or biological explanation at present. Ecologically, however, it is adaptive: the closest seedling was usually under the (now incinerated) parent crown of non-sprouters whereas those of resprouters were on average four times further away.ConclusionsOur study highlights the value of recognizing four reproductive syndromes within fire-prone vegetation, and shows how these are characterized by marked differences in their seedling–adult spatial relations that serve to enhance biodiversity of the community.

The annual herb Parthenium hysterophorus L. (Asteraceae), remains one of Southern Africa's most significant invasive weeds, commonly invading savannas, and their rangelands, causing severe losses to agriculture, livestock production and native biodiversity. Previous studies have suggested that perennial grasses may act as useful competitive species, capable of suppressing the growth and invasion of P. hysterophorus. To explore this, a total of 48 plots were established within an invaded savanna, using a randomised block design, and included treatments with and without the clearing of P. hysterophorus, as well as with and without the sowing of native perennial grass seed (Anthephora pubescens, Chloris gayana, Cynodon dactylon, Digitaria eriantha, Eragrostis curvula, Panicum maximum and Themeda triandra). Plots were assessed yearly in terms of P. hysterophorus density and growth as well as grass species composition, basal cover, and biomass over a three-year period. Clearing alone was found to exacerbate invasion, increasing P. hysterophorus density by 40%. Whereas the sowing of grass seed, in both the cleared and uncleared plots, increased the abundance of perennial grass species by 28%, subsequently reducing the size, reproductive output and density of P. hysterophorus over the three years. In addition, these sowing efforts contributed towards partial restoration of the plots, enhancing grass basal cover by ~15% and biomass production by 17%. Overall, this research suggests that sowing of native grass species, with or without clearing, may be a useful supplementary control or restoration tool towards the long-term management of P. hysterophorus invasions in managed savannas and rangelands in Southern Africa.

This Commentary is a response to a Commentary published in the May/June 2020 issue: Nattrass N. Why are black South African students less likely to consider studying biological sciences? S Afr J Sci. 2020;116(5/6), Art. #7864, 2 pages. https://doi.org/10.17159/sajs.2020/7864 Responses to the Commentary in the May/June 2020 issue have been published collectively in a special issue of Volume 116.

Serotiny is the prolonged storage of seeds in closed cones or fruits held within the crown of woody plants. It is widespread throughout fireprone vegetation with a predominantly winter rainfall, especially in Mediterrnanean-type ecosystems (MTEs). Nonstorage is a feature of fireprone vegetation with summer-dominant rainfall or nonfireprone vegetation. Serotiny confers fitness benefits on an individual when fire return intervals fall between age to reproductive maturity and the plant life span. The level of serotiny within and between species varies greatly along a continuum indicating highly plastic responses to different environmental conditions. Here we review how and why the traits that underpin this reproductive syndrome evolved and continue to control the occurrence of species in contemporary landscapes. We documented 1345 serotinous species in fireprone regions of Australia, South Africa, the Mediterranean Basin, North America, and Asia. The length of seed storage varies from a few years (weak serotiny) to >10 years (strong serotiny), with remarkable diversity even within clades. We show how the interplay between postfire and interfire seedling recruitment dictates the expression of serotiny along a strong serotiny/nonserotiny continuum, and that, where strong serotiny is favored, the ‘gene support for serotiny’ builds up over successive generations. Nonserotiny is favored in the absence of fire or occurs at intervals exceeding plant longevity, but also when the fire is so frequent that only resprouters can survive. We identify 23 traits associated with serotiny/nonserotiny syndromes that are subject to both environmental and phylogenetic constraints. While all are coordinated for maximum fitness, some traits, such as protection from granivores, are only indirectly related to the fire regime. Serotiny has a long history extending back to the Triassic. The rate of serotinous-lineage proliferation has fluctuated greatly over time but peaked over the last 5 million years. Nonserotinous species have evolved from serotinous ancestors in response to increased fire frequency, or as plants migrated to fire-free habitats. We note that contemporary shifts in climate, land-use, and exploitation have had a profound, but disproportionate, effect on the conservation status and evolutionary trajectory of serotinous species in MTEs. Escalating anthropogenic impacts increase the need to understand how and why serotiny is such a prominent feature of some fireprone ecosystems. We highlight avenues for future research and argue for the use of temporally based measures of serotiny to facilitate comparisons between studies.

More frequent and intense climate hazards, a predicted outcome of climate change, are likely to threaten existing livelihoods in rural communities, undermining households’ adaptive capacity. To support households’ efforts to manage and reduce this risk, there is a need to better understand the heterogeneity of risk within and between communities. The Intergovernmental Panel on Climate Change revised their climate vulnerability framework to incorporate the concept of risk. This study contributes toward the operationalization of this updated framework by applying a recognized methodology to the analysis of the climate-related risk of rural households. Using a mixed-method approach, including a cluster analysis, it determined and assessed archetypical patterns of household risk. The approach was applied to 170 households in two villages, in different agroecological zones, in the Vhembe District Municipality of South Africa’s Limpopo Province. Six archetypical climate-risk profiles were identified based on differences in the core components of risk, namely, the experience of climate hazards, the degree of exposure and vulnerability, and the associated impacts. The method’s application is illustrated by interpreting the six profiles, with possible adaptation pathways suggested for each. The archetypes show how climate-related risk varies according to households’ livelihood strategies and capital endowments. There are clear site-related distinctions between the risk profiles; however, the age of the household and the gender of the household head also differentiate the profiles. These different profiles suggest the need for adaptation responses that account for these site-related differences, while still recognizing the heterogeneity of risk at the village level.

Pereskia aculeata Miller (Cactaceae) is a primitive leafy cactus indigenous to Central and South America that has become a problematic invasive alien plant elsewhere in the world. In South Africa the plant invades established forests, clearings, thickets and plantations along the southern and eastern higher rainfall regions of the country. Pereskia aculeata is a woody vine (liana) that scrambles up existing vegetation competing for resources, often causing canopies to collapse under its weight. Similarly, to other invasive vines, mechanical and chemical control is challenging due to the plant growing intertwined with indigenous vegetation and therefore, biological control using specialist insect herbivores is considered essential for its management. Increasing atmospheric carbon dioxide (CO2) concentrations are expected to favour weeds, however this response is likely to be influenced by projected changes to rainfall patterns. Pereskia aculeata were grown from truncheons for five months at three CO2 concentrations: 250 (sub-ambient), 400 (ambient) and 600 (elevated) ppm under two watering regimes, reduced-water (200 ml wk-1) and ambient-water (400 ml wk-1), to simulate two annual rainfall scenarios of ~520 mm (below present optimal) and ~1040 mm (present optimal), respectively. Elevated CO2 (eCO2) increased growth rates, biomass accumulation and reduced leaf nutritional quality (nitrogen content and C:N ratios), but only for ambient-water treatment plants. Nevertheless, higher photosynthetic rates under eCO2 improved water use efficiency for both water treatments, which was greatest for the reduced-water treatment plants. Management of P. aculeata in South Africa is already extremely challenging and with rising atmospheric CO2, P. aculeata has the potential to become more problematic, particularly in optimal rainfall areas. Furthermore, with improvements in water use efficiency, P. aculeata has the potential to expand into lower rainfall areas, although it is unlikely to pose the same risk as those plants invading higher rainfall sites.

LiDAR data collection was funded by the Andrew Mellon Foundation, the Council for Scientific and Industrial Research (CSIR) Strategic Research Panel and the Department of Science and Technology (DST). The CAO has been made possible by grants and donations from the Avatar Alliance Foundation, Margaret A. Cargill Foundation, David and Lucile Packard Foundation, Gordon and Betty Moore Foundation, Grantham Foundation for the Protection of the Environment, W. M. Keck Foundation, John D. and Catherine T. MacArthur Foundation, Andrew Mellon Foundation, Mary Anne Nyburg Baker and G. Leonard Baker Jr, and William R. Hearst III. B. F. N. E. is supported by the Exxaro Chairman's Fund. P. J. M. is funded by the DST/NRF Centre of Excellence in Tree Health Biotechnology and an NRF Innovation Scholarship (grant UID: 95030).

Foraging site selection by large herbivores is influenced by multiple factors varying across landscapes and spatial scales. Termite mounds harbour highly nutritious plants compared with the savanna matrix, making them preferred foraging patches in many savannas. However, it is unknown whether termite mounds equally influence herbivore grazing intensity across geological substrates and mound sizes. These knowledge gaps hamper our ability to draw general trans-ecosystem conclusions about the effect of termite mounds for savanna herbivores. We measured grazing intensity on mounds of three different size classes (small, medium and large) across two geologies with differing soil nutrition (granite and basalt) in Gonarezhou National Park, Zimbabwe. We recorded measurements across three seasons (hot wet, cool dry and hot dry), and at multiple distances from mounds. Grazing intensity on mounds was higher on nutrient-poor granite than nutrient-rich basalt, and termite mounds of all sizes had a significant effect on grazing on granite during the cool dry season. Grazing was highest on large mounds on both geologies throughout the year. Large mounds also had the largest spatial influence on grazing in the cool dry season, up to 8 m beyond the mound edge on granite and 2 m on basalt. When scaled up to the landscape level, mounds influenced about 15% of the granite landscape, but only about 0.5% of the basalt landscape. Our results show that the positive effects of mounds on grazing intensity were pronounced on nutrient-poor soils but negligible on nutrient-rich soils, and that the magnitude of these effects varied across seasons and with mound size.

The annual shrub, Parthenium hysterophorus L. (Asteraceae), is a severe noxious weed of global significance, having been the target of control programmes in several affected countries. Biological control efforts in South Africa have seen a total of four agents released to date, one of the most promising of which is the leaf-feeding beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), first released in 2013. Detailed study of the ecophysiological interactions of insect herbivores and their target weeds are under-represented in the biological control literature. Extensive leaf-feeding by Z. bicolorata adults metabolically impaired P. hysterophorus leaves, resulting in a ∼36% reduction to photosynthesis in remaining leaf tissue. However, in response to Z. bicolorata herbivory, adjacent undamaged leaves showed an up-regulation in photosynthesis of ∼11%. Photosynthetic reduction was attributed to the removal of leaf tissue, physiological impairment and increased microbial abundance resulting from Z. bicolorata . Zygogramma bicolorata was found to increase the number of bacterial and fungal microbes present on P. hysterophorus leaves. Despite the ability to photosynthetically up-regulate in response to herbivory, P. hysterophorus is unlikely to overcome the physiological implications associated with continued Z. bicolorata feeding and the increase in microbes. Given the potential effectiveness of Z. bicolorata as a biological control agent, efforts should be made to maximise incidence of the beetle in the field.

In savanna ecosystems, tree canopy patches differ in plant species composition compared to adjacent intercanopy spaces due to different levels of resource availabilities. Mistletoes further augment nutrients underneath tree canopies whilst reducing their hosts’ competitive edge, thus providing more resources and creating patches that support higher understory species richness. However, little is known on how understory species and functional trait assemblages, in both canopy and intercanopy spaces, are affected by varying overstory mistletoe infection intensities. This study investigated how functional and species diversity/composition varied within and between canopy patches and intercanopy spaces of high- and low mistletoe-infected Vachellia karroo trees. The affinity of individual species to the different canopy patches and intercanopy spaces was also assessed. Microhabitats had significantly different species compositions. A higher proportion of species (34%) showed a strong positive affinity towards canopy patches whilst intercanopy spaces were strongly associated with only 9% of recorded species, indicating greater dominance of some species there. Generally, subcanopy patches had significantly higher species richness and diversity, and functional diversity, compared to adjacent intercanopy spaces. These variables increased with increasing mistletoe infection, thus grass, forb and tree species diversity were 17–43% higher, and functional diversity indices were 0.5–28% greater in high- compared to low mistletoe-infection canopy patches. Furthermore, species richness and diversity of C3, C4, annual and perennial plants were 1.27–3.13-fold higher within canopy patches compared to intercanopy spaces and 1.28–1.74-fold greater within high- compared to low mistletoe-infection microhabitats. Consequently, high mistletoe-infection canopy patches had between 1.08 and 3.76-fold greater species richness and diversity of C3, C4, annual and perennial plants compared to the other three microhabitats. Our findings suggest that by enhancing spatial heterogeneity, variations in mistletoe infection facilitate biodiversity and to a lesser extent vegetation structural diversity in these semi-arid savannas.

QUESTIONS: The degree to which renosterveld shrublands are fire‐dependent is currently unclear. To address this issue, the following questions were asked: (1) does smoke stimulate germination of soil‐stored seeds in renosterveld; (2) does recently‐burned renosterveld display changed composition and higher diversity than unburned vegetation; and (3) how do the species compositions of renosterveld soil seed banks and standing vegetation compare? LOCATION: Swartland, Cape Floristic Region, South Africa. METHODS: Soil seed bank samples from a north‐ and south‐facing slope were smoke‐treated and germinated to test for smoke‐stimulated germination. Burned standing vegetation was surveyed 16 months post‐fire, as was unburned vegetation on the same slopes. Seed bank species richness and density were compared between smoke‐treated and untreated samples within and between slopes. Burned and unburned standing vegetation were compared within and between slopes in terms of species richness, abundance and aerial cover. Compositional similarity of the seed banks and standing vegetation was assessed. RESULTS: Seed banks were dominated by annuals and graminoids. Smoke treatment had no effect, except for driving significantly higher species richness and seedling density in south‐facing slope perennial shrubs. Species richness and seedling density were significantly higher in seed banks on the south‐facing slope compared to the north‐facing slope. Burned standing vegetation exhibited significantly higher diversity than unburned vegetation. Annuals and graminoids displayed significantly higher species richness and aerial cover in burned renosterveld. The north‐facing slope contained less than half the number of species/m² compared to the south‐facing slope. The seed banks and standing vegetation showed low to intermediate similarity (Sorensen = 31%–53%), but grouped close together on an NMDS plot, suggesting intermediate similarity overall. CONCLUSIONS: Elevated germination of perennial shrubs in smoke‐treated seed bank samples and increased diversity of post‐fire standing vegetation suggest the renosterveld in this study shows elements of a fire‐driven system. Certain species only recruited in burned sites, suggesting fire‐stimulated germination. Aspect had a major influence on plant community composition, with the mesic south‐facing slope being more diverse than the xeric north‐facing slope. The similarity between the seed banks and standing vegetation was higher than previously shown for renosterveld, and appears to be higher than for fynbos.

The invasive tree Solanum mauritianum Scopoli remains one of the world’s most widespread environmental weeds. Despite biocontrol providing one of the few viable long-term solutions to tackling S. mauritianum invasions globally, only South Africa and, more recently, New Zealand, have programmes in place. Ongoing biocontrol efforts against S. mauritianum are reviewed here with particular reference to South Africa. The South African programme has suffered a troubled history, with considerable research efforts culminating in the eventual release and establishment of only two insect agents, Gargaphia decoris Drake and Anthonomus santacruzi Hustache. The difficulties experienced have hindered research into new agents, causing apprehension in using biocontrol internationally. However, recent studies have demonstrated that biocontrol may be deserving of renewed investment, particularly within an integrated management context. In this review, we advocate for the revival of the S. mauritianum biocontrol programme in South Africa, and discuss possible avenues for future research internationally.

The long observed disparity in fruit production among individual trees of the iconic African baobab, Adansonia digitata L. presents a potential challenge for the supply of fruit and seeds for food, medicinal and cosmetic purposes. Moreover, this disparity presents an unsolved mystery with ecological as well as economic implications. African baobabs are hermaphrodites where flowers have both male and female reproductive organs within the same flower. Here we evaluate the reproductive features, pollen-pistil interactions, and pollinator-attractant traits from South African baobabs to investigate whether trees with different fruit production levels have different floral features. We show that morphological traits highlight functional sex differences that match with average fruit production data of our sampled trees. Trees that produce more fruit comprised more functionally female flowers, whereas more functionally male flowers were characteristic of trees that did not produce many fruits. This difference may signify a shift in sex allocation in African baobabs, which suggests that baobabs might be functionally, or cryptically, dioecious. Collectively our data suggest that maintaining both tree types within a landscape is paramount for long-term sustainable harvesting of baobab fruit and seeds.

Water hyacinth (Eichhornia crassipes Mart. Solms Pontederiaceae) mainly occurs as a free-floating aquatic plant, but can survive decreasing water levels when rooted in soil. This adaptation to seasonal fluctuations in hydrology may contribute to its invasive potential in natural and man-made water bodies, where stranded plants can take root. To understand how water hyacinth plants rooted in saturated-soil compared to floating conspecifics, we conducted a month long mesocosm growth experiment in a well fertilised outdoor pool (experiment one) comparing plant traits between treatments. Following this, we investigated the effect of water stress on the plants rooted in soil, by conducting a progressive and prolonged drought (experiment two). We simultaneously investigated the effect of nutrient depletion in the mesocosm, on both the floating plants and those in saturated-soil. Plant physiological parameters were measured on these treatments. Plants were re-watered after the drought to assess mortality at two different drought intensities. Floating plants produced a larger total leaf area compared to plants rooted in saturated-soil, however, plants in both treatments developed a similar number of leaves and ramets. Progressive drought reduced photosynthesis, which was attributed to both stomatal and metabolic limitations. Nutrient stress reduced photosynthesis more in floating plants than rooted plants, and these reductions in photosynthesis were solely attributed to metabolic limitations caused by a decreased chlorophyll content. Plants recovered from prolonged drought but not prolonged severe drought. Water-stressed water hyacinth exhibited a drought avoidance strategy, a trait which may contribute to its ability to persist in variable aquatic environments.

Concerns exist over the continual decline of marula trees (Sclerocarya birrea subsp. caffra), a large ecologically and economically important tree species in southern Africa, primarily as a consequence of impact by African elephants (Loxodonta africana) and poor regeneration. We assessed changes to marula tree population structure in a protected area that was only recently opened to elephants. Jejane Private Nature Reserve (JPNR) has been subjected to elephants from the Greater Kruger National Park (Greater KNP) since 2013, as it was fenced off beforehand. A previous survey of the marula population in JPNR was done in 2009 and again in 2016. Therefore this study aimed to (i) assess elephant-induced impact and mortality levels on the previously surveyed JPNR marula tree population, (ii) compare these levels with previously recorded impact and mortality levels on marula trees across the Greater KNP, and (iii) assess marula seed predation and seedling recruitment in JPNR. The resurveyed marula population had declined by 23.8% post-elephant movement into JPNR, with the highest annual mortality rates (AMR) and elephant impact scores for trees in the 5–8 m height class. The JPNR marula tree AMR of 8.1% was higher than that of Greater KNP (4.6%). Only two marula seedlings were found across all transects, whilst 84.2% of all endocarps’ locules had seeds missing, with bite marks present on 42.3% of all endocarps. This suggests potential high levels of seed predation and a lack of seedling recruitment. The concern over the impact by elephants on adult marula trees is therefore escalated as a consequence of the lack of regeneration, primarily because of seed and seedling predation. Management policies should be focused on protection methods for individual trees, seedlings and seeds, together with a large scale artificial surface water management plan to manipulate herbivore densities and pressures on marula tree populations.

Termites are recognised soil ecosystem engineers in the tropics and sub-tropics, making the understanding of their distribution a priority. However, there is a poor understanding of how differences in soil properties and plant biomass productivity affect termite species diversity. We compared the diversity of termites between two soils of differing geological provenance (basalt and granite), and consequently contrasting nutrient content, but subject to similar climatic conditions in a semi-arid Zimbabwean savanna. Basaltic soils contained more dead wood, and were more nutrient-rich than granitic soils, with significantly higher exchangeable Ca and Mg, and available P, and a less acidic pH. However, despite this higher soil nutrient status on basalts, functional and taxonomic termite diversity was higher on granites, although termite abundance was similar between the geological formations. Termite assemblages differed between the geological formations, with very little overlap. We conclude that termite diversity is highly influenced by soil productivity, with nutrient-poor soils having higher diversity, potentially due to reduced competitive exclusion or differences in species adaptation to soil conditions.

Questions Termite mounds are well known to host a suite of unique plants compared with the surrounding savanna matrix. However, most studies testing the significance of mounds for ecosystem heterogeneity have been conducted at single sites. Mound effects on savanna heterogeneity across varying landscapes are less well understood, and how effects might vary across geological types and mounds of different sizes is as yet unknown. Location Gonarezhou National Park, Zimbabwe. Methods We studied effects of termite mounds on vegetation spatial heterogeneity across two geologies (granite and basalt), including effects of mound size and the spatial extent of termite influence. Herbaceous vegetation was sampled on mounds and savanna matrix plots, and along distance transects away from mounds. Soil nutrients on mounds and in the matrix were also compared between geologies. Results Soil nutrients were more concentrated in large mounds compared with the matrix on granite, but not on basalt, with mounds therefore acting as nutrient hot-spots on nutrient-poor granite only. Large and medium sized mounds hosted compositionally different grass species to the matrix on granite, but not on basalt. Large mounds on granite also had significantly lower grass and forb species richness compared with the matrix. However, small mounds on granite, and all mound size categories on basalt, did not have an effect on grass and forb species richness or assemblage composition, an observation attributed to a lack of difference in soil nutrients between the mounds and matrix. Conclusion Our study shows that the significance of termite mounds to ecosystem spatial heterogeneity is strongly influenced by geology and mound size, with mound effects on herbaceous plant species heterogeneity more pronounced in dystrophic geologies and around large mounds. Future studies should take greater cognisance of landscape context and mound size when seeking to understand the contribution of termite mounds to ecosystem structure and function. This article is protected by copyright. All rights reserved.

Africa hosts a rich assemblage of cycads: 66 Encephalartos species, Stangeria eriopus and Cycas thouarsii. Most Encephalartos and S. eriopus adults appear to be fire-tolerant, and certain Encephalartos species may be fire-dependent. Four Encephalartos species and S. eriopus are primarily insect-pollinated. African cycad populations typically have sex ratios of 1:1, with very small populations often male-biased. Coning is typically infrequent and erratic, with many species exhibiting mast-seeding. Viable seed production in Encephalartos populations tends to decline with decreasing population size, and seed predation by weevils is common. Seed dispersal in Encephalartos is usually localized, but vertebrates may facilitate dispersal over longer distances. Stem material of 25 Encephalartos species and S. eriopus is used for traditional medicine, primarily in South Africa. Two-thirds of Africa’s cycad species are threatened, with four species already Extinct in the Wild. The illegal acquisition of cycads from wild populations is the principle threat to their persistence. Further research is recommended on seed and fire ecology, population dynamics, and the outcomes of conservation interventions.

The regeneration ecology of many southern African threatened plant species is poorly understood. Temperature is considered the most important environmental factor governing seed germination. The germination temperature requirements of the critically endangered stem succulent, Adenium swazicum, were determined under controlled conditions, together with tetrazolium staining protocol tests to assess seed viability. The effects of soil medium, watering levels, depth of sowing and shading on germination/seedling emergence were also determined at the Lowveld National Botanical Garden (LNBG). Germination/seedling emergence was compared under nursery conditions within (Skukuza Nursery in Kruger National Park) and outside (LNBG) the natural distribution range of A. swazicum. The germination of viable seeds ranged 96.5–100% for a broad range of temperatures from 20 to 35 °C as well as for 30/20 °C (light/dark) alternating temperature. No germination was recorded at 5 °C and 10 °C, and relatively limited germination at 15 °C (42.9%) and 40 °C (15.4%). These results were modelled using a Generalized non-linear model, with a binomial error and a logit link function, best-fit models were second-order polynomials (i.e., quadratic). Mean Germination Time ranged from 2 to 6 days among temperature treatments. Tetrazolium together with germination results for the 20 − 35 °C temperatures showed moderate to high seed viability across populations and between years within the same population. Seedlings readily emerged irrespective of soil media (3 types) or planting depth (surface, 5 and 10 mm) but higher emergence occurred under more frequent watering. Seedlings emerged equally well under sun or shade conditions, but only subsequently survived in the shade. Despite lower temperatures recorded during October/November 2010 at LNBG (outside range: 27.2 ± 0.9 °C) compared to Skukuza (within range: 32.6 ± 0.9 °C), final germination/seedling emergence was high at both locations (LNBG: 82%; Skukuza: 94%). Together with field observations, this study shows that (a) seed germination is rapid and with high percentages after being cued by warm to hot summer temperatures, a period when rainfall is also at its highest, and (b) that seedling recruitment depends on the availability of suitably shaded microsites. This is the first study on the regeneration ecology of an Adenium sp. and will aid both in situ and ex situ conservation of A. swazicum.

The African baobab's ( Adansonia digitata ) breeding system has not been experimentally verified, and it remains unclear why such a stark disparity exists between ‘male’ trees that produce few, if any, fruit, and ‘female’ trees that produce many fruit consistently year after year. Combined results from gene flow analyses of 26 trees scored for nine microsatellite loci and hand-pollination experiments on five trees across three baobab populations in Mutale District, Limpopo Province, South Africa, investigated the breeding system, strength of incompatibility within trees, and if genetic differentiation was detectable between ‘males’ and ‘females.’ Our data suggest that A. digitata is largely self-incompatible. ‘Male’ and ‘female’ trees showed high heterozygosity and estimated outcrossing rates did not differ in degree of self-incompatibility, and showed no significant genetic differentiation. The ability of ‘males’ to produce fruit if cross-pollinated suggests that poor fruit production in male trees is most likely due to low rates of pollination.

Weed biological control programmes frequently make use of flower feeding agents to reduce the fruit and seed output of invasive plants. Florivorous species have the potential for both direct and indirect effects on the reproductive success of their target plants. The flowerbud-feeding weevil, Anthonomus santacruzi , was first released in South Africa during 2008 for biological control of an invasive tree, Solanum mauritianum . This study assessed the impact of A. santacruzi florivory as well as the potential of the agent to act as an indirect pollinator. Floral damage caused by A. santacruzi was trivial, with only ∼5% of the anther and ∼2% of petal areas being removed. However, the subsequent effects of A. santacruzi were considerably more damaging, with 25% and 66% reductions in the flowering and fruiting of S. mauritianum inflorescences respectively. Additionally, fruit produced from inflorescences exposed to A. santacruzi were smaller in size, with fewer viable seeds. This suggests that in areas with well-established A. santacruzi populations, the agent may facilitate the self-pollination and subsequent inbreeding of S. mauritianum.

Humans have played a major role in altering savanna structure and function, and growing land-use pressure will only increase their influence on woody cover. Yet humans are often overlooked as ecological components. Both humans and the African elephant, Loxodonta africana, alter woody vegetation in savannas through removal of large trees and activities that may increase shrub cover. Interactive effects of both humans and elephants with fire may also alter vegetation structure and composition. Here we capitalize on a macroscale experimental opportunity - brought about by the juxtaposition of an elephant-mediated landscape, human-utilized communal harvesting lands and a nature reserve fenced off from both humans and elephants - to investigate the influence of humans and elephants on height-specific treefall dynamics. We surveyed 6 812 ha using repeat, airborne high resolution Light Detection and Ranging (LiDAR) to track the fate of 453 685 tree canopies over two years. Human-mediated biennial treefall rates were 2-3.5 fold higher than the background treefall rate of 1.5% treefall ha-1 yr-2, while elephant-mediated treefall rates were 5 times higher at 7.6% treefall ha-1 yr-2 than the control site. Model predictors of treefall revealed that human or elephant presence was the most important variable, followed by the interaction between geology and fire frequency. Treefall patterns were spatially heterogeneous with elephant-driven treefall associated with geology and surface water, while human patterns were related to perceived ease of access to wood harvesting areas and settlement expansion. Our results show humans and elephants utilize all height-classes of woody vegetation, and that large tree shortages in a heavily utilized communal land has transferred treefall occurrence to shorter vegetation. Elephant- and human-dominated landscapes are tied to interactive effects that may hinder tree seedling survival which, combined with tree loss in the landscape, may compromise woodland sustainability. This article is protected by copyright. All rights reserved.

Phenology of African savannas is considered to have high temporal variability, yet few studies have quantified this variation between seasons. This study assessed the weekly green-up phenology of trees, as well as below- and between-canopy grasses in a broad-leaved savanna woodland in the Nylsvley Nature Reserve (NNR), South Africa over three growing seasons (2012–2014). Tree green-up start dates were highly variable in comparison to the grasses, whose green-up showed close ties to the availability of water, particularly rainfall. Early green-up of Burkea africana trees occurred if rainfall onset was after mid-October, thus long-term rainfall records indicate that trees would benefit from early-greening approximately 46% of the time in the NNR. The effects of tree canopies on the growth and biomass accumulation of below-canopy grasses showed that during periods of irrigation when water was not limited, light availability became the limiting factor for grass growth, with grasses below the higher shading of B. africana producing significantly lower biomass than those below the less shaded Terminalia sericea canopies. Access to higher light conditions at the start of the growing season potentially drives the 2–5 days faster green-up of below-canopy grasses compared to the between-canopy grasses. A comparison of the above phenological data to the remotely sensed normalized difference vegetation index (NDVI) was made, to determine if it was possible to detect an early-greening signal from the trees, which the sensor was able to effectively distinguish. This study highlights the variability in temporal separation between tree and grass phenology in an African savanna. Trees take advantage of periods of low competition from herbaceous neighbours at the end of the dry season prior to the onset of seasonal rainfall, and potentially at the end of the growing season when seasonal rainfall concludes through the uncoupling of their green-up cue from seasonal water availability.

Reducing the reproductive output of an invasive weed using biocontrol can result in a decrease in population density and help control the spread of the weed. Two biocontrol agents, a stem gall fly, Procecidochares utilis (Tephritidae), and a leaf-spot fungal pathogen, Passalora ageratinae (Mycosphaerellaceae), have been released against Crofton weed, Ageratina adenophora, in South Africa. In this study we investigated the impact of the agents, individually and together, on Crofton weed’s reproductive output, under both greenhouse and field conditions. Galling by P. utilis, with or without P. ageratinae, resulted in 32% fewer flowering structures per stem, compared to ungalled treatments in both the field and the greenhouse; however, without P. utilis, P. ageratinae did not reduce the number of flowering structures per stem. In the greenhouse, galled stems had 24% (single-galled)-55% (double-galled) fewer filled achenes than ungalled stems, while pathogen-infected stems had 27% fewer filled achenes per stem in comparison to uninfected stems. Although the biocontrol agents reduced the number of filled achenes, the percentage germination remained high and similar for all treatments (69.3–74.4%) in the field and the greenhouse. The combination of the two agents together did not provide more control of sexual reproduction than P. utilis alone. However, Crofton weed compensates for galling with increased sideshoot growth (vegetative reproduction), which in time also flower. But P. ageratinae inhibits growth of sideshoots. Therefore, the combination of the two agents best enhances the level of control rather than either agent in isolation.

The flowerbud-feeding weevil, Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), was released in 2008 as a biological control agent against the South American invasive tree Solanum mauritianum Scop. (Solanaceae), in South Africa. The weevil has since established in two localities, namely along the KwaZulu-Natal South Coast and around the Sabie region of Mpumalanga. Recent releases on the Highveld region (Johannesburg and Pretoria) have been unsuccessful to date. This study aimed to test the hypothesis that climate, particularly low temperature and low relative humidity, restricts the survival and establishment of A. santacruzi in South Africa. The survival of A. santacruzi adults in relation to low temperatures and relative humidities was assessed in the laboratory. Climate analyses revealed that matches of